# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1246877396 -3600
# Node ID 3a5d8601293c95f7d783fef3a5f8282fd68603f2
# Parent d33a665b2c05b0785637330074c285034571faf1
x86 shadow: Fix lock-less race between resync and fast path.
Signed-off-by: Gianluca Guida <gianluca.guida@xxxxxxxxxxxxx>
---
xen/arch/x86/mm/shadow/multi.c | 48 ++++++++++++++++++++---------------------
1 files changed, 24 insertions(+), 24 deletions(-)
diff -r d33a665b2c05 -r 3a5d8601293c xen/arch/x86/mm/shadow/multi.c
--- a/xen/arch/x86/mm/shadow/multi.c Mon Jul 06 11:48:44 2009 +0100
+++ b/xen/arch/x86/mm/shadow/multi.c Mon Jul 06 11:49:56 2009 +0100
@@ -2975,6 +2975,30 @@ static int sh_page_fault(struct vcpu *v,
#if (SHADOW_OPTIMIZATIONS & SHOPT_FAST_FAULT_PATH)
if ( (regs->error_code & PFEC_reserved_bit) )
{
+#if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC)
+ /* First, need to check that this isn't an out-of-sync
+ * shadow l1e. If it is, we fall back to the slow path, which
+ * will sync it up again. */
+ {
+ shadow_l2e_t sl2e;
+ mfn_t gl1mfn;
+ if ( (__copy_from_user(&sl2e,
+ (sh_linear_l2_table(v)
+ + shadow_l2_linear_offset(va)),
+ sizeof(sl2e)) != 0)
+ || !(shadow_l2e_get_flags(sl2e) & _PAGE_PRESENT)
+ || !mfn_valid(gl1mfn = _mfn(mfn_to_page(
+ shadow_l2e_get_mfn(sl2e))->v.sh.back))
+ || unlikely(mfn_is_out_of_sync(gl1mfn)) )
+ {
+ /* Hit the slow path as if there had been no
+ * shadow entry at all, and let it tidy up */
+ ASSERT(regs->error_code & PFEC_page_present);
+ regs->error_code ^= (PFEC_reserved_bit|PFEC_page_present);
+ goto page_fault_slow_path;
+ }
+ }
+#endif /* SHOPT_OUT_OF_SYNC */
/* The only reasons for reserved bits to be set in shadow entries
* are the two "magic" shadow_l1e entries. */
if ( likely((__copy_from_user(&sl1e,
@@ -2983,30 +3007,6 @@ static int sh_page_fault(struct vcpu *v,
sizeof(sl1e)) == 0)
&& sh_l1e_is_magic(sl1e)) )
{
-#if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC)
- /* First, need to check that this isn't an out-of-sync
- * shadow l1e. If it is, we fall back to the slow path, which
- * will sync it up again. */
- {
- shadow_l2e_t sl2e;
- mfn_t gl1mfn;
- if ( (__copy_from_user(&sl2e,
- (sh_linear_l2_table(v)
- + shadow_l2_linear_offset(va)),
- sizeof(sl2e)) != 0)
- || !(shadow_l2e_get_flags(sl2e) & _PAGE_PRESENT)
- || !mfn_valid(gl1mfn = _mfn(mfn_to_page(
- shadow_l2e_get_mfn(sl2e))->v.sh.back))
- || unlikely(mfn_is_out_of_sync(gl1mfn)) )
- {
- /* Hit the slow path as if there had been no
- * shadow entry at all, and let it tidy up */
- ASSERT(regs->error_code & PFEC_page_present);
- regs->error_code ^= (PFEC_reserved_bit|PFEC_page_present);
- goto page_fault_slow_path;
- }
- }
-#endif /* SHOPT_OUT_OF_SYNC */
if ( sh_l1e_is_gnp(sl1e) )
{
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